Temperature probes are used in many applications for measuring the temperature of various objects and environments. U.S. Pat. Nos. 6,592,253 and 7,168,330, in which the Applicant is an inventor, describe prior art embodiments of a temperature probe or combination pressure/temperature transducer, or combination pressure/temperature/flow transducer, respectively.
The fastest thin film resistive temperature device (RTD) elements currently available today for use in temperature probes are not very suitable for high speed measurements in the medical field as well as in environments that are corrosive or hostile, as their thermal time constant ranges somewhere between 50 ms and 200 ms, or even longer. Additionally, the thermal time constants are not consistent and can vary considerably from manufacturing lot to lot.
A thin film RTD element's thermal time constant determines a temperature probe's response time to temperature measurements and thus, determines its speed. Speed can be an important consideration when selecting a temperature probe, especially in medical applications where the invasive nature of the measurement, or the particular needs of the patient, may limit the time available to make the measurement. The ability to make high speed temperature measurements also is important in corrosive or hostile environments where prolonged exposure to the media or environment can damage the probe.
One accepted definition of the thermal time constant of a temperature probe of any type is the time in seconds, or milliseconds, that it takes the probe's sensor, such as a thin film RTD element, to sense and respond to a temperature change of 63.2% of a specific temperature range. Another accepted definition is the length of time that it takes the probe to sense a temperature change from 10% to 90% of a specific temperature range.
A widely accepted temperature range for the measurement and calibration of the time constant of a thin film RTD, for example, is the temperature range represented by an agitated ice bath at the lower end and boiling water at the upper end, i.e. 0° C. and 100° C., respectively. These two temperatures are often used as a calibration or test temperature range because they are relatively easy to generate and to maintain.
While the thermal time constants of prior art thin film RTDs have improved, the improvements have not kept pace with developments in other areas of technology and the associated need to measure temperatures more quickly and in more unstable and hostile environments.
Past experience also indicates that the construction of a thin film RTD element generally is not consistent, as the size of the protective glass beads on the best products available can and do vary considerably, resulting in inferior temperature probe performance.
Past experience strongly indicates that a new approach is needed in the development and design of very fast thin film RTD elements for applications in the very high speed measurement of critical temperatures in extremely corrosive and hostile environments, or in a medical environment.
These and other benefits are realized with the very high speed thin film RTD element of the present invention.